Support member for high-temperature heat-treated metal molding object and process for production thereof

ABSTRACT

A carbonaceous support member for a high-temperature heat-treated metal molding object, particularly a setter for heat-treatment in powder metallurgy, is formed as a carbon-ceramic composite shaped product having a bulk density of 1.2-1.6 g/ml and including a carbonaceous matrix and 3-20 wt. % of ceramic particles which are uniformly dispersed in the carbonaceous matrix and partly exposed to the surface of the composite. The support member can effectively prevent carburization of a metal molding object supported thereby during the heat-treatment without causing a problem of peeling of coating layer as encountered in a ceramic-coated support member. The support member may be prepared by compression molding of a powdery mixture of a fine carbon precursor and ceramic particles, followed by heating at 1000-2000° C. to carbonize the fine carbon precursor.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a carbonaceous support member used forsupporting a metal molding object heat-treated at high temperatures, anda process for producing the support member.

Powder metallurgy is a process of compressing metal powder to form ashaped powder compact and heat-treating the shaped compact at hightemperatures to provide a sintered and shaped metal object. Accordingly,the powder metallurgy is better in mass-productivity and much moreexcellent in product yield than other production processes and istherefore widely used as a process for providing, e.g., steel-mademechanical parts, such as cams and shafts for automobiles. Acarbonaceous support member, which is light and has an excellent thermalconductivity, is used as a support plate (setter) for supporting such ashaped metal powder compact to be sintered in a reducing ornon-oxidizing atmosphere in the powder metallurgy (as disclosed in,e.g., Japanese Laid-Open Patent Application (JP-A) 8-198685), or aholding member for a metal shell ring used in sealing of electronicparts with fused glass (as disclosed in, e.g., JP-A 5-319929). Such acarbonaceous support member for heat-treating high-temperature heatedmetal object is required of freeness from carburization (a phenomenon oftransfer of carbon as by diffusive penetration into solid metal) into ahigh-temperature heat-treated metal object, as an important property, inaddition to thermal impact resistance for enduring a repetition ofheating to 800° C. or higher and cooling. These requirements areparticularly intense in the case of treating metal objects of iron(Fe)-based metals, inclusive of: Fe alone, and Fe alloys comprisingprincipally Fe together with graphitization-promoting elements, such asnickel (Ni), cobalt (Co), aluminum (Al) and silicon (Si), or otheralloying elements.

For example, the carburization occurring in the heat treatment of ametal powder compact is assumed to proceed as follows. As is well known,carbon (C) forms a solid solution with iron to provide an iron alloyhaving a remarkably reduced melting temperature. Accordingly, if carbonof a setter for sintering a metal powder compact diffuses into thepowdery metal to form a solid solution, the melting point of the metalis lowered to cause the melt-sticking of the metal object to the setter.If the metal object once melt-sticks to the carbonaceous setter, thecontact area between the metal and the carbon is increased to promotethe carburization, thereby further lowering the melting point of themetal, until the metal object completely melts down in extreme cases.

Some proposals have been made for preventing the above-mentionedcarburization phenomenon.

For example, by noting that non-graphitizable carbon is effective forsuppressing the carburization, there have been proposed a shaped plateof glass-like carbon (amorphous carbon) that is a carbonized product ofa thermosetting resin as the starting material (JP-A 10-67559), and apress-molded and calcined product of particulate non-graphitizablecarbon after coating with a thermosetting resin (JP-A 2002-154875).Until now, however, the use of such a carbon structure different fromgraphite has not succeeded in providing a sufficient effect ofsuppressing the carburization.

Ti, Nb, V, Ta, W, Mo, Cr, Mn, etc., are known as metal elements having astronger affinity with carbon than Fe, and it is possible to prevent thecarburization if the carbonaceous setter is coated with a film ofcarbide of these metal elements, e.g., by plasma flame spraying.However, such a coated setter is liable to cause peeling of the coatingfilm from the setter because of a difference in thermal expansioncoefficient between the film and the carbonaceous setter substrate whensubjected to a repetition of heating-cooling cycle. The peeling of thecoating film can be alleviated if the film is made thinner but, in thiscase, the coating is liable to be lost by wearing during the use.

Several proposals have been made to prevent the carburization bysurface-coating a carbonaceous setter with a ceramic layer. For example,these proposals include: a method of coating with chromic acid, followedby calcination to form a chromium oxide film (JP-A 2-212385), a methodof press-bonding a paper-like sheet principally comprising ceramicpowder under heating (JP-A 8-198685), and a method of plasma-sprayingyttrium oxide (Y₂O₃)(JP-A 2000-509102, JP-A 2002-179485). However, anyof such ceramic coating films as proposed above cannot endure arepetition of a cycle of heating to a high temperature and cooling dueto a difference in thermal expansion coefficient with the substratecarbonaceous plate, thus exhibiting only a limited life.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems of known materials, an object ofthe present invention is to provide a support member for a metal objectfree from the peeling of film or coating under a repetition ofheat-treatment of metal molding object in powder metallurgy and otherprocesses and yet capable of effectively preventing the carburizationeven at a temperature of 1000° C. or higher, particularly a setter forheat treatment in the powder metallurgy.

Another object of the present invention is to provide an effectiveprocess for production of such a carbonaceous support member.

As a result of our study for achieving the above-mentioned objects, wehave discovered that a carbon-ceramic composite product obtained byappropriate compression-molding and heat-treatment of a carbon precursorand a certain ceramic material (used herein as excluding a carbonmaterial though a carbon material is classified under ceramics in somecases), provides a support member for metal object exhibiting anexcellent carburization suppression effect, thus arriving at the presentinvention.

According to the present invention, there is provided a support memberfor a high-temperature heat-treated metal molding object, comprising: acarbon-ceramic composite shaped product comprising a carbonaceous matrixand 3-20 wt % of ceramic particles uniformly dispersed in thecarbonaceous matrix and partly exposed to a surface of thecarbon-ceramic composite shaped product, said carbon-ceramic compositeshaped product having a bulk density of 1.2-1.6 g/ml.

Such a support member for metal molding object of the present inventioncan be produced through a process including: molding a dispersivemixture of a fine carbon precursor and ceramic particles to form acompact under pressure, and heat-treating the compact to carbonize thecarbon precursor at 1000-2000 ° C.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, the function of the support member for high-temperatureheat-treated metal molding object is described more specificallyprincipally with reference to a setter for heat treatment in powdermetallurgy, as a representative embodiment thereof.

The setter for heat treatment in powder metallurgy according to thepresent invention is free from the problem of peeling of a ceramic layeras encountered in a conventional setter formed by coating a carbon platewith a ceramic layer. Peeling between two different materials is causedin proportion to a slip distance determined as a product of (a boundarylength)×(a difference in thermal expansion coefficient) or caused by amagnitude of slipping (or shearing) stress between the two materialsproportional to the slip distance. Accordingly, a shearing stress aslarge as causing peeling does not occur between a matrix carbonaceousmaterial and a ceramic particle which has an extremely small adhesionboundary length with the carbonaceous matrix compared with a coatingceramic layer.

The setter for heat treatment in powder metallurgy according to thepresent invention exhibits a better carburization prevention effect thana setter comprising a carbon plate alone, presumably because the ceramicparticles obstruct the contact between the carbon and a metal moldingobject causing the carburization. Further, the ceramic particles aredispersively present in the entire body (carbonaceous matrix) of thesetter. Accordingly, even if a superficial layer of the setter is wornout, the ceramic particles are successively exposed to the surface ofthe setter to reduce the lowering in carburization prevention effect.

The setter for heat treatment in powder metallurgy of the presentinvention contains only a small amount of 3-20 wt. % (which correspondsa half or below in member of percentage by volume if a difference inspecific gravity between carbon and ceramic is taken into account).Accordingly, the surface exposure rate of the ceramic particles is verylow, whereas the ceramic particles exhibit a good carburizationprevention effect. We assume the reason as follows.

In the setter of the present invention which is a carbonized product ofa compression-molded compact of a dispersive mixture of a fine carbonprecursor and ceramic particles, a portion of the carbon precursor islost by evaporation during the carbonization to cause a shrinkage of thecarbonaceous matrix, thus leaving projections of ceramic particles atthe surface of the resultant setter, whereby even a relatively smallamount of ceramic particles can effectively suppress the contact betweencarbon and metal object which is a cause of the carburization. For thispurpose, ceramic particles having an appropriately large primaryparticle size of 50-500 μm are preferred so as to provide projectionsexhibiting a strength capable of supporting the weight of the metalmolding object. Further, the surface ceramic particles may be lostaccompanying the wearing and surface burning of the setter, whereas theceramic particles are allowed to remain as projections since the burningloss is preferentially caused with respect to the carbonaceous matrixthan the ceramic particles.

Another assumption as follows is possible in view of the mechanism ofcarburization. Carburization is a phenomenon of carbon dissolving into ametal, such as iron. For example, in the case where an iron-based metalpowder compact is placed on a setter of carbonaceous material andheat-treated, the heat treatment is performed at 1100-1200° C. In thiscase, carburization proceeds as follows. Pure iron has a melting pointabove 1150° C. but the melting point is lowered down to ca. 1150° C. ascarbon diffuses into the iron by carburization. As carburization occursat a contact point between the carbon plate and the metal moldingobject, the portion of the metal contacting the carbon plate is causedto have a lower melting point, and if the heat treatment temperatureexceeds 1150° C., the metal portion melts and sticks to the carbonplate. As the lowest portion of the metal object melts, the metal objectsinks by its own gravity to increase the contact portion with the carbonplate and promote the carburization until the metal object melts down.As is understood from the above explanation, the carburization ispromoted by a cycle of phenomena including a lowering in melting pointdue to carburization, an increase of contact portion between metal andcarbon due to the lowering in melting point and an increase incarburization reaction area due to the increase in contact portion.Accordingly, it is assumed that if carburization once occurs at acontact point between carbon and metal, the carburization proceedsprogressively due to successive occurrence of phenomena in theabove-mentioned cycle.

It is assumed most effective to cut off the above-mentioned cycle inorder to suppress the carburization at a contact point between a carbonplate and a metal object. In the setter of the present invention whereinceramic particles hardly reacting with a metal are disposed at anappropriate proportion in the setter, even if carbon and metal reactwith each other locally, the sinking of the metal object due to meltingof the lower portion of the metal object is suppressed owing to thecontact with ceramic which is free from carburization, so that thecarbon supply rate to the metal object is remarkably lowered toremarkably suppress the carburization. This is another assumption forexplaining the effective function of the support member of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The support member for metal object, particularly the setter for heattreatment in powder metallurgy, of the present invention can be preparedby mixing a fine carbon precursor with ceramic particles, molding theresultant mixture under pressure to form a compact, and heat-treatingthe compact at 1000-2000° C. The following description will be madeprincipally with reference to the setter for heat-treatment in powdermetallurgy as a principal embodiment of the support member forhigh-temperature heat-treated metal object.

The fine carbon precursor may be prepared by appropriately heat-treatingpitches of coal or petroleum origin, various thermosetting resins, etc.,followed by conversion into a fine form as desired. The fine carbonprecursor may have a shape of fiber or particles (inclusive of spheres).Fibrous carbon precursor may be added in order to strengthen the setter.If the fiber length is too short, a sufficient strength cannot beattained, and if too long, the molding of the setter becomes difficult.The fibrous carbon precursor may preferably have a number-average fiberdiameter of 7-30 μm and a number average fiber length of 0.05 -7 mm,more preferably 0.09-0.5 mm. Further, the particulate (inclusive ofspherical) ceramic particle may preferably have an average particle size(a diameter giving cumulatively 50% by volume) of 150 μm-2mm,particularly 0.3-1 mm.

The carbon precursor is converted into a carbonaceous material (matrix)by heat treatment. The texture of the carbonaceous matrix as a majorcomponent of the setter largely depends on the texture of the carbonprecursor. In the present invention, the texture of the carbonaceousmatrix formed by the heat treatment of the carbon precursor is notparticularly restricted, but may preferably comprise non-graphitizablecarbon which causes isotropic thermal expansion and shrinkage on heatingand cooling, respectively.

An example of carbon precursor for providing a non-graphitizablecarbonaceous matrix particularly preferably used in the presentinvention may be prepared as follows.

That is, a pitch, such as petroleum pitch or coal pitch, is mixed underheating with an additive comprising an aromatic compound of two or threearomatic rings having a boiling point of at least 200° C. or a mixtureof such aromatic compounds, and the mixture is then shaped to provide ashaped pitch product. Then, the additive is removed from the shapedpitch product by extraction with a solvent having a low dissolving powerto the pitch and a higher dissolving power to the additive, to leave aporous pitch product, which is then oxidized to provide an infusibilizedproduct. After the infusibilization or at any stage proceeding thereto,the product is rendered fine to provide a fine non-graphitizable carbonprecursor. The above-mentioned aromatic additive may for examplecomprise one or a mixture of two or more species selected fromnaphthalene, methylnaphthalene, phenylnaphthalene, benzylnaphthalene,methylanthracene, phenanthrene and biphenyl. The addition amount thereofmay preferably be in the range of 30-70 wt. parts per 100 wt. parts ofthe pitch. The mixing of the pitch and the additive may be performed ina molten state under heating in order to accomplish uniform mixing. Themixture of the pitch and the additive may preferably be shaped intoparticles having a size of 1 mm or smaller. The shaping may be performedin a molten state or, e.g., by pulverization, after cooling.

Suitable examples of the solvent for removing the additive from themixture of the pitch and the additive may include: aliphatichydrocarbons, such as butane, pentane, hexane and heptane; mixturescomprising principally aliphatic hydrocarbons, such as naphtha andkerosene; and aliphatic alcohols, such as methanol, ethanol, propanoland butanol.

By extracting the additive from the shaped mixture product with such asolvent, it is possible to remove the additive from the shaped productwhile retaining the shape of the product. At this time pores are formedat sites from which the additive is removed, thereby providing auniformly porous pitch product.

The thus-obtained porous pitch product is then subjected to oxidation(infusibilization) with an oxidizing agent to develop a crosslinkingtexture, thereby providing a non-graphitizable carbon precursor. Theoxidation treatment may be performed at a temperature of preferably100-400° C. Examples of the oxidizing agent may include:

oxidizing gases, such as O₂, O₃, SO₃, NO₂, mixture gases formed bydiluting these gases with, e.g., air or nitrogen, and air; and oxidizingliquids, such as sulfuric acid, nitric acid, and hydrogen peroxideaqueous solution.

In the present invention, a non-graphitizable carbon precursor asproduced in the above-described manner and ceramic particles may bemixed and compressed into a precursor compact, which may be heat-treatedat a temperature of at least 1000° C. and at most 2000° C. in anon-oxidizing atmosphere. It is however necessary to optimize theprecursor compact in order to provide a setter of a good quality forheat treatment in powder metallurgy. If the precursor compact or shapedbody contains too much volatile matter, gas evolution during the heattreatment becomes excessive so that discharge of the evolved gas insidethe compact becomes difficult to cause a rupture of the setter. On theother hand, if the volatile matter is too small in amount, this means ashortage of binder component, and the adhesion between the particlesduring the heat treatment is insufficient, thus failing to provide asufficiently strong setter for heat treatment in powder metallurgy. Theprecursor compact may preferably have a volatile matter content of 5-30wt. %, more preferably 10-25 wt. %.

In order to control the volatile matter and binder component in thecarbon precursor, it is preferred to mix an additional carbon precursor,such as a pitch or a thermosetting resin. It is particularly preferredto coat the above-mentioned non-graphitizable carbon precursor with athermosetting resin. In order to uniformly attach the ceramic particlesto the surface of the non-graphitizable carbon precursor, it isparticularly preferred to simultaneously effect the surface-coating ofthe non-graphitizable carbon precursor with a thermosetting resin andthe attachment of ceramic particles onto the non-graphitizable carbonprecursor. The coating with a thermosetting resin imparts a roomtemperature adhesiveness not possessed by the fine carbon precursor anda compression-moldability to the fine carbon precursor, and at the timeof calcination, the thermosetting resin per se is carbonized so as tofill the gap or void in the fine carbon precursor, thereby providing anon-graphitic carbon product integral with the carbonized product of thenon-graphitizable fine carbon precursor. In this instance, it ispreferred to coat 95-60 wt. parts of the fine carbon precursor with 5-40wt. parts of thermosetting resin (giving a total of 100 wt. parts withthe carbon precursor). If the thermosetting resin is below 5 wt. parts,it is difficult to sufficiently attain an intended addition effect ofthe thermosetting resin, and in excess of 40 wt. parts, too muchvolatile matter is evolved during the calcination to cause a foaming ofthe compact (or molded product), thus being liable to fail in providinga prescribed shape of non-graphitic carbon-ceramic composite product. Atthe time of calcination, a thermosetting resin exhibits a highpercentage of carbonization into non-graphitic carbon and can easilyform a good carbon/ carbon composite with the carbonized product of thefine carbon precursor, so that it is preferred than a thermo-plasticresin. The fine carbon precursor and the thermosetting resin bothprovide carbonized products of similar non-graphitic textures, thusproviding a non-graphitic carbon material which is entirely uniforminclusive of uniformity of thermal expansion coefficient and excellentin thermal impact resistance, after the calcination. The thermosettingresin may preferably be liquid at least partially, and examples thereofmay include: phenolic resin, furan resin, unsaturated polyester resin,and polyimide resin (precursor). Among these, phenolic resin ispreferred. In a particularly preferred embodiment, the fine carbonprecursor is first surface-coated with resole-type liquid phenolicresin, and the novolak-type solid phenolic resin is attached thereto.

The ceramic particles are incorporated in the product setter ofcarbon-ceramic composite material for the purpose of obstructing acontact between carbon in the setter and a metal powder compact duringheat treatment for sintering the compact.

Accordingly, if the content of the ceramic particles in the setter forheat treatment in powder metallurgy is too small, the effect ofobstructing the contact between the metal compact and the carbon isliable to be scarce, and if the content is excessively large, theproduct setter for heat treatment in powder metallurgy is liable tocause a lowering in strength either being undesirable. Accordingly, thesetter for heat treatment in powder metallurgy may preferably have acontent of ceramic particle of at least 3 wt. % and at most 20 wt. %.From the viewpoint of suppressing a breakage due to thermal expansionand shrinkage of the setter during the repetition of heat treatment, theceramic particles may preferably be uniformly dispersed in thecarbonaceous matrix while exposing a portion thereof to the surface ofthe setter.

The ceramic particles to be added may comprise any kind of ceramicsinclusive of, for example, oxide-form ceramics and nitride-formceramics, as far as they hardly react with metals comprising iron oroxides thereof in the temperature region for sintering in powdermetallurgy. As for the particle size of the ceramic particles, too smalla particle size exhibits only a scarce effect of suppressing the contactbetween the metal object and the carbon of the support member. Too largea particle size results in a decrease in number of contact between thecarbon and the carbonaceous matrix leading to a reduction in strengthand a breakage of the setter due to a difference in thermal expansionand shrinkage between the carbonaceous matrix and the ceramic particles.Accordingly, the ceramic particles may preferably have an averageparticle size (a particle size giving cumulatively 50% by volume) of 50-500 μmm, more preferably 80-300 μm. It is further preferred that atleast 20 wt. % of the ceramic particles have particle sizes in theabove-mentioned range for the average particle size. Some types ofceramic particles, e.g., a certain form of alumina, can form secondaryparticles by agglomeration or melt-sticking of primary particles. Insuch a case, the above-mentioned particle size refers to a primaryparticle size in the present invention. For a similar reason, theceramic particles used in the present invention may preferably compriseprimary particles free from secondary agglomeration. Even if the ceramicparticles have a secondary particle size of 50 μm or larger, they can bereduced into primary particles due to a stress exerted during thedispersive mixing with the fine carbon precursor and compressionmolding, or a load exerted from the metal object during the heattreatment, thus being liable to fail in exhibiting the intended particlesize effect. It is necessary for the ceramic particles have a meltingpoint higher than the temperature for sintering the metal powdercompact, preferably a melting point of at least 1300° C., morepreferably at least 1500° C. As an example of ceramic material complyingwith such requirements, it is preferred to use particles of alumina orfused alumina formed by melt-fusion of alumina-based starting material,followed by pulverization. As for the purity, the alumina particles maypreferably have a high alumina purity, also from the viewpoint ofobviating the commingling of impurities to the metal powder compact,preferably at least 90 wt. %, further preferably at least 95 wt. %.

The fine carbon precursor and the ceramic particles are mixed andcompression-molded to form a compact (i.e., a precursor of supportmember). The compression molding may preferably be performed at roomtemperature or at an elevated temperature of up to 250° C. under apressure of 0.5-30 MPa. The compact or precursor is then heat-treated(calcined) to provide a support member, such as a setter. If thecalcination temperature is below 1000° C., the carbonization of thecarbon precursor as a principal component of the compact is liable to beinsufficient, and a temperature in excess of 2000° C. is liable topromote a reaction between the added ceramic particles and the finecarbon precursor or can possibly exceed the melting point of the ceramicparticles. The calcination temperature may preferably be 1000-1800° C.,further preferably 1200-1600° C.

An average layer-plane spacing according to X-ray diffractometry is agood measure of texture of carbonaceous material constituting thethus-produced support member. More specifically, the carbonaceousmaterial constituting the setter of the present invention may preferablyhave a 002-plane layer spacing (d₀₀₂) of at least 0.34 nm.

The handling of a support member, particularly a setter forheat-treatment in powder metallurgy, becomes easier, if it is lighter inweight, but if it is too light, voids in the setter are liable to belarger, thus resulting in a weaker strength. Accordingly, the supportmember containing ceramic particles of the present invention maypreferably have a bulk density of 1.2- 1.6 g/ml. If the bulk density isbelow 1.2 g/ml, it becomes difficult to attain a sufficient strength.Above 1.6 g/ml, the setter is liable to have an increased number ofcontacts with the metal molding object thereon. It is also a preferredthat the support member, particularly the setter, has a bending strengthof at least 15 MPa.

EXAMPLES

Hereinbelow, the present invention will be described more specificallywith reference to Examples and Comparative Examples. Physical propertiesdescribed herein including the following Examples are based on valuesmeasured according to the following methods.

(1) Average Layer-Plane Spacing (d₀₀₂) of Carbonaceous Material

A powdery sample of a carbonaceous material is packed in analuminum-made sample cell and irradiated with monochromatic CuKα rays(wavelength λ=0.15418 nm) through a graphite monochromator to obtain anX-ray diffraction pattern. The peak position of the diffraction patternis determined by the center of gravity method (i.e., a method whereinthe position of a gravity center of diffraction lines is obtained todetermine a peak position as a 2θ value corresponding to the gravitycenter) and calibrated by the diffraction peak of (111) plane ofhigh-purity silicon powder as the standard substance. The d₀₀₂ value iscalculated from the Bragg's formula shown below.

d ₀₀₂=λ/(2·sin θ)  (Bragg's formula)

(2) Volatile Matter Content

According to a fixed carbon content measurement method described in JISK2425 (Testing method for creosote oil, processed tar, and tar pitch), afixed carbon content at 800° C. of a sample is measured, and a volatilematter content is calculated by subtracting the fixed carbon contentfrom the initial weight of the sample.

(3) Average (Primary) Particle Size

Three drops of a dispersant (a cationic surfactant; “SN DISPERSANT7347C”, made by Sun Nopco Co.) are added to ca. 0.1 g of a sample to wetthe sample with the dispersant. Then, 30 ml of pure water is added tothe sample, and the mixture is dispersed for ca. 2 min. by an ultrasonicwasher to form a primary particle dispersion liquid, which is thensubjected to a measurement of particle size distribution in a particlesize range of 0.1-1000 μm by means of a particle size measurementapparatus (“MICROTRACK FRA-9220”, made by Nikkiso K.K.), thereby obtaina 50%-cumulative volume-average particle size.

(4) Ceramic Content in a Setter

A sample setter is burnt at 1000° C. in air to leave a residue, and theweight of the residue regarded as the ceramic weight is divided by theweight of the sample to provide a ceramic content.

(5) Evaluation of Carburization

A powdery alloy of iron 59 wt. %, graphite 1 wt. %, nickel 20 wt. %, andcobalt 20 wt. %, is compression-molded under a pressure of 100 MPa intoa disk-shaped metal powder compact of 20 mm in diameter and 5 mm inthickness. The thus-prepared metal powder compact is placed on a sampleof carbonaceous setter for heat-treatment in powder metallurgy and heldat 1150° C. or 1200° C. for 1 hour in a nitrogen atmosphere to sinterthe metal powder compact. Then, the surfaces of the sintered product andthe setter were observed to evaluate the presence or absence ofcarburization (i.e., surface roughening or color change). The resultswere evaluated according to the following standard.

-   A: No carburization is observed.-   B: Carburization is observed on at least one of the sintered product    and the carbonaceous setter.-   C: The sintered metal product is melted to leave a trace of    distortion on the setter sample in a shape corresponding to the    sintered product.

Example 1

83 wt parts of a spherical infusibilized pitch of petroleum originhaving an average particle size of 0.62 mm (“KH-1B, made by KurehaChemical Industry

Co., Ltd.; oxygen content=7.1%, fixed carbon content =72.1%, specificvolume of open pores=ca. 0.05 g/ml) as a non-graphitizable carbonprecursor, was surface-coated with 6 wt. parts of resole-type liquidphenolic resin (“RESITOP PL-4804”, made by Gun Ei Chemical Industry Co.,Ltd.). Then, 8 wt. parts of novolak-type solid phenolic resin(“PG-2411”, made by Gun Ei Chemical Industry Co., Ltd.; average particlesize=20-80 μm) and 3 wt. parts of alumina powder (“ALUNDUM PARTICLES#80”, made by K.K. Nikkato; Al₂O₃ content=at least 99%, average particlesize=200 μm), were attached to the resole-coated carbon precursorparticles to provide a molding material. The molding material wascharged in a flat mold and molded at a pressure of 5 Mpa and at 170° C.or above for 15 min. to form a ca. 7 mm-thick plate-shaped compact. Theplate-shaped compact was further heat-treated at 150° C. for 24 hours tocure the phenolic resin. The thus-treated plate compact was laid flat ina graphite crucible and was placed together with the crucible in a kiln,and after vacuum evacuation, heat-treated (calcined) at 1450° C. (for 1hour under a nitrogen gas stream to obtain a setter for heat treatmentin powder metallurgy having sizes of 420 mm×250 mm×6 mm. The setterexhibited a bulk density of 1.43 g/ml.

As a result of the evaluation of carburization described above, thethus-obtained carbon-ceramic composite setter exhibited no carburizationat either of 1150° C. and 1200° C. and was found to be a satisfactorysetter for sintering a metal molding object thereon.

The composition and representative properties of the setter aresummarized in Table 1 appearing hereinafter together with those ofExamples and Comparative Examples described below.

Example 2

A setter for heat-treatment in powder metallurgy was prepared in thesame manner as in Example 1 except for changing the composition ofstarting materials for the plate-shaped compact to 81 wt. parts of thespherical infusibilized pitch of petroleum origin, 6 wt. parts of theresole-type liquid phenolic resin, 8 wt. parts of the novolak-type solidphenolic resin, and 5 wt. parts of the alumina powder.

Example 3

A setter for heat-treatment in powder metallurgy was prepared in thesame manner as in Example 1 except for changing the composition ofstarting materials for the plate-shaped compact to 79 wt. parts of thespherical infusibilized pitch of petroleum origin, 6 wt. parts of theresole-type liquid phenolic resin, 8 wt. parts of the novolak-type solidphenolic resin, and 7 wt. parts of the alumina powder.

Example 4

A setter for heat-treatment in powder metallurgy was prepared in thesame manner as in Example 1 except for changing the composition ofstarting materials for the plate-shaped compact to 76 wt. parts of thespherical infusibilized pitch of petroleum origin, 6 wt. parts of theresole-type liquid phenolic resin, 8 wt. parts of the novolak-type solidphenolic resin, and 10 wt. parts of the alumina powder.

Comparative Example 1

A setter for heat-treatment in powder metallurgy was prepared in thesame manner as in Example 1 except for changing the composition ofstarting materials for the plate-shaped compact to 80 wt. parts of thespherical infusibilized pitch of petroleum origin, 6 wt. parts of theresole-type liquid phenolic resin, and 14 wt. parts of the novolak-typesolid phenolic resin, and omitting the alumina powder.

Comparative Example 2

A setter for heat-treatment in powder metallurgy was prepared by cuttinga commercially available extruded graphite material (“PS-G12”, made byK.K. S.A.C.) into a plate measuring 420 mm×250 mm×6 mm.

Reference Example

A setter for heat-treatment in powder metallurgy was prepared in thesame manner as in Example 2 except for using 5 wt. parts of aluminapowder (“A12”, made by Nippon Keikinzoku K.K.; alumina content=at least99%, average particle size=1 μm) instead of 5 wt. parts of the aluminapowder (“ALUNDUM PARTICLES #80”, made by K.K. Nikkato; Al₂O₃ content=atleast 99%, average particle size=200 μm).

The composition and representative properties of the setters prepared inthe above Examples, Comparative Examples and Reference Example aresummarized in Table 1 below.

TABLE 1 Ceramic particles Primary Carbonaceous Setter particle matrixBulk Content size d₀₀₂ density Carburization Example Species (wt. %)(μm) (nm) (g/ml) 1150° C. 1200° C. 1 Alumina 4.0 200 0.365 1.43 A B 2Alumina 6.7 200 0.365 1.43 A B 3 Alumina 9.3 200 0.365 1.44 A B 4Alumina 13.3 200 0.365 1.46 A A Comp. 1 None 0.0 — 0.365 1.42 C C Comp.2 None 0.0 — 0.338 1.72 C C Reference Alumina 6.7  1 0.365 1.43 C C

As described above, according to the present invention, there isprovided a support member, particularly a setter for heat-treatment inpowder metallurgy capable of effectively preventing carburization of ametal molding object supported during high-temperature heat treatment ofthe metal molding object supported thereby without causing a problem ofpeeling of a coating layer as encountered in the case of aceramic-coated support member. Such a support member can be preparedthrough a simple process wherein a dispersion mixture of a fine carbonprecursor and ceramic particles is compression-molded, and thenheat-treated at a temperature of 1000-2000° C. to carbonize the carbonprecursor.

1-7. (canceled)
 8. A process for producing a metal molding object, comprising providing a support member in a form of a carbon-ceramic composite shaped product comprising a carbonaceous matrix and 3-20 wt. % of ceramic particles uniformly dispersed in the carbonaceous matrix and partly exposed to a surface of the carbon-ceramic composite shaped product, said carbon-ceramic composite shaped product having a bulk density of 1.2-1.6 g/ml; forming a shaped metal powder compact; placing the shaped metal powder compact in contact with the partly exposed ceramic particles of the support member; heating the shaped metal powder compact together with the support member at a temperature of 800° C. or higher in a reducing or non-oxidizing atmosphere to sinter the metal powder compact; and cooling and recovering the sintered metal powder compact as the metal molding object in separation from the support member.
 9. The process according to claim 8, wherein the ceramic particles have a primary particle size of 50-500 μm.
 10. The process according to claim 8, wherein the ceramic particles comprise fused alumina having an alumina purity of at least 90 wt. %.
 11. The process according to claim 8, wherein the metal molding object is a steel-made mechanical part.
 12. The process according to claim 8, wherein the support member is provided by molding a mixture of a fine carbon precursor and ceramic particles under pressure to form a compact, and heat-treating the compact at a temperature of 1000-2000° C. to carbonize the carbon precursor.
 13. The process according to claim 12, wherein the mixture of the fine carbon precursor and the ceramic particles is formed by dispersively attaching the ceramic particle together with a thermosetting resin onto the surface of the fine carbon precursor and then molded under pressure.
 14. The process according to claim 13, wherein the thermosetting resin comprises a liquid thermosetting resin.
 15. The process according to claim 14, wherein the fine carbon precursor is first, coated with the liquid thermosetting resin, and then a solid thermosetting resin and the ceramic particles are attached to the fine carbon precursor, followed by the molding under pressure. 